Engine spark control apparatus

ABSTRACT

This disclosure relates to apparatus for operating a combustion engine by controlling the spark ignition voltage to said engine. Said control is created by the application of two opposing currents to the input of an amplifying device which is used to selectively shunt a constant current source away from the control electrode of a second amplifying device connected to control the formation of said ignition voltage.

This is a division of application Ser, No. 226,298, filed July 7, 1988,now U.S. Pat. No. 4,821,702, which is a continuation of application Ser.No. 112,100, filed Oct. 22, 1987, now U.S. Pat. No. 4,774,924.

This invention relates to an electronics system for controlling theformation of a spark used to ignite a fuel air mixture in an engine andcreates or removes said spark in response to electrical signalsavailable within the battery charging and or ignition system of saidengine.

BACKGROUND OF THE INVENTION

Systems for selectively inabling or disabling the ignition to combustionengines to correspond with various operating conditions or to supplydesired ignition to the engine under all allowable normal operatingconditions have been know in the art. Two examples would be applicants,U.S. Pat. Nos. 3,802,400 and 4,664,080. A thorough understanding of theteaching of those patents is essential to the proper understanding ofthis application since the concepts clearly describe therein will not beherein repeated. Those patents are incorporated herein by reference.

It is an object of this invention to increase the accuracy over thegreatest range of engine operating conditions while maximizing thereliability, and minimizing the cost of components within the system. Anoperating condition of particular concern is the temperature range overwhich the system must operate. It should be realized that with thechange in the state of the art of combustion engines and the morecompact in the spaces into which they are sometimes mounted compared toart of even a few years ago, that the temperature extremes to whichengines associated electronics are exposed has increased.

Another object of this invention is to reduce the number of connectionsof this control apparatus to the existing vehicle and ignition systemwiring.

DESCRIPTION OF THE DRAWINGS

The above and other objects, and features of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is a diagram of a portion of a currently known vehicle wiringsystem.

FIG. 2 is a circuit diagram of a preferred embodiment of this inventionshowing connection points to the circuit of FIG. 1.

FIG. 3 is a circuit diagram of another version of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 is a portion of a wiring diagram for a three or four wheeledrecreational vehicle of the type presently being produced in theindustry. Points labeled A and B have been added to show the connectionto similarly labeled points on FIG. 2. Only the portions of theelectrical wiring already on the vehicle that connect to and interactwith circuit of the present invention are shown. The alternator in FIG.1 is typically a permanent magnet alternator driven by the crank shaftof the engine not shown. It supplies power for the electrical systemssuch as for lighting and starting on the vehicle. The charging of thebattery by the alternator is controlled by the SRC and regulator controlcircuit shown in FIG. 1. It is desirable to place the SCR with its anodegrounded because of the advantageous heat sinking of the SCR. Thisresults in neither alternator lead grounded making sensing of alternatorvoltage for speed measuring purpose more difficult. This type of batterycharging regulator is shown in applicant's U.S. Pat. No. 4,490.779.However, one skilled in the art could also adapt this control apparatusto other types of regulators which might be used in these vehicles.Since one side of the alternator is permanently connected to thebattery, the voltage at point B will be the alternator voltagesuperimposed upon the battery voltage. If the alternator is of thepermanent magnet type both the frequency and the open circuit voltage ofthe alternator will change linearly with engine speed. The negativeportion of the alternator waveform from point B to ground will beselectively clipped by the SCR of FIG. 1 in response to the amount ofcharge needed by the battery, however the positive portion of thatwaveform will remain essentially at its open circuit value. The ignitionsystem shown typically derives its power from a separate winding on thealternator, however, could derive its power from another source such asthe battery. Switch one is the existing switch which is used to shortcircuit an ignition system lead to ground to stop the engine. The waveform shown in C1 indicates that the ignition stop wire has a pulsatingDC voltage going positive with respect to ground. An ignition system ofthis type is shown in applicant's U.S. Pat. No. 3,566,188. Wherein thecathode of diode 16 would be point B. If it is desired to have thecontrol circuit of this invention limit engine speed only under certainconditions a switch could be placed between point A of FIG. 1 and thecorresponding connection point A of FIG. 2. Without such a switch thecontrol apparatus would be operable at all times to prevent destructiveoverspeed of the engine in case the load was lost. Two possible examplesof switches in the lead connecting the 2 point A's would be a switchclosed when the transmission was put in reverse to limit the speed ofthe vehicle in reverse only, or a switch closed when the manuallyoperated throttle level was released thus slowing the engine down to thepresent limit even if the connection linkage, normally a throttle cable,from the hand actuated lever to the carburetor or other engine powercontrol, was stuck or frozen in the open position. Similarly,appropriate switching could be used to accomplish both the previouslymentioned functions.

FIG. 2 shows a circuit diagram of an electric control apparatusconstructed in accordance with this invention. FIG. 3 shows anotherversion of this invention also useable above the maximum temperaturecapabilities of SCR type devices. Points labeled A and B are to beconnected directly to the similarly labeled points of the existingvehicle wiring system of FIG. 1, with the option all inclusion of theadditional switch discussed previously. The waveform at point A is thealternator voltage superimposed on the battery voltage, with a portionof the negative going part of the waveform clipped depending on thestate of the charge of the battery. There is a small but finiteinteraction between the clipping of this negative portion of thewaveform and the positive portion of the waveform leading to some lossin accuracy of the previously referred to patents. In the presentinvention this waveform is applied effectively to resistor R1 and zenerdiode Z1 in series to ground. Typical value stated for understandingpurposes only would be a 3K 1/4 watt resistor for R1 and a 18 volt 1/4watt zener for Z1. It can be seen by one skilled in the art that theoperating condition of Z1 is a very conservative level, neither near theknee of the zener characteristic, or at excessively high wattage. Manycircuits known in the art operate zener diodes in the input (typicallybase) circuit of amplifying devices that requires very criticalselection of the zener diodes. The voltage across Z1 will then be arectangular waveform clipped in the positive direction at the zenervoltage, that is approxiamtely 18 volts, and in the negative directionat the forward voltage drop of the zener. (approximately 0.7 volt) Thevoltage across this zener therefore can be considered as beingequivalent of the AC voltage source shown as A-1 in previously referredto U.S. Pat. No. 3,802,400. The waveform across Z1 has the advantage ofbeing much more stable with variations and alternator load and otherfactors, such as alternator tolerance or temperature, compared toconnecting this point directly to the alternator. The positive portionof this waveform is rectified with the diode D1, and capacitor C2 isthus charged to approxiamtely +17.3 volts DC. The component types wouldbe a 1 MF capacitor for C2, and a type 1N4148 diode for D1. Capacitor C2thus serves to filter this voltage to produce a DC level whicheliminates the need for the separator connection shown with a plus signin the figure of U.S. Pat. No. 3,802,400. This voltage is then appliedthrough resistor R3 to the gate of SCR1. Typical value of R3 might be300,00 ohms allowing approximately 50 microamps of current to flow tothe gate of SCR1. This current is sufficient to turn on devices readilyavailable in the commercial market place. Since the voltage to turn SCR1is very low compared to the voltage on capacitor C2, the current flowingthrough R3 can be considered as a constant current source as viewed fronthe SCR gate and cathode terminals. Transistor Q1, shown as a N channeljunction field effect transistor, is connected from the gate terminal ofSCR1 to ground. As is known, a device of this type is on or in theconducting state when a positive or 0 voltage is preset from the gate tothe surface terminals, and turns off when a negative voltage of knownampitude is applied to the gate terminal with respect to the sourceterminal. Thus current flowing through resistors R2 and R4 is in thedirection to bias Q1 to conduct thus shunting the current flowingresistor R-3 away from the gate of SCR1 and to ground. This isparticularly advantageous at very high operating temperatures since theeffective impedance from the drain to the source of Q1 when in the onstate is lower that could feasibly be used for resistor R3 in U.S. Pat.No. 3,802,400 or resistor R5 in U.S. Pat. No. 4,664,080, thus allowingan improvement in high temperature stability of the circuit. CapacitorC1, diodes D2, and D3, serve as a frequency to voltage or currentconverter as is known, and is also pointed out in U.S. Pat. No.3,802,400, and will not be further described here. It should be realizedthat diodes D2, and D3 need to be of a low leakage type. Capacitor C1might typically be 4,000 pf. Capacitor C3 serves to filter or averagethe opposing output of the positive current through R2 and R4 and thenegative current produced by the network of C1, D3 and D4. The valuechosen will depend on the response speed needed, 0.1MF could be typicalbut is stated as are all preceding values only for understanding thecircuit. Resistors R2 and R4 are shown as two components in series as aneasy means of accurately calibrating the circuit. For instance, R4 mightbe a 1.3megohm resistor it would be the same in all units in a givenproduction run. R2 might vary from near 0 to 200,000 ohms selectedeither on an individual basis to compensate for variations in othercomponents such as primarily C1 and Q1. C1 and Q1 could alternately besorted on a lot basis and a R2 value selected for each such lot. Thecircuit of this invention has appreciably better accuracy than thecircuit of U.S. Pat. No. 4,664,080 since it senses the frequency and notthe voltage of the alternator, thus alternator tolerances are almostcompletely removed. It also has an appreciable improvement in accuracyover the circuit of U.S. Pat. No. 3,802,400 since in that patent boththe base emitter drop of transistor T and the gate cathode voltage tofire the SCR are effectively in series with the control currents wherein the present application the source and gate of transistor Q1 aredirectly across the output or summing point of those opposing currents.FIG. 3 shows a modification of this invention suitable for extremelyhigh temperature operation. Similar functioning components have the samedesignations as in FIG. 2. Stable operation of this version of thisinvention has been observed to over 165° C. SCR1 is replaced by a PNPtransistor Q2, and a NPN transistor Q3, and a resistor R5. Q2 and Q3 areconnected in a known configuration giving junctions in the PNPNconfiguration typical of a SCR but eliminating the resistance within theterminal gate region of a SCR. Resistor 5 establishes a preselectedcollector current, and therefore, approximate emitter current for Q3 atthe turn on point of the combination. This regenerative turn on pointoccurs because the output or collector of Q2 is connected to the inputor base of Q3 and the output of Q3 is connected to the input of Q2. Oneskilled in the art could of course substitute other semiconductordevices. The current at the regenerative turn on point is predictablebased on the base emitter voltage required to turn on Q2 and the valueof R5. Thus the operating point of zener diode Z2 is controlled at apreselected level. The voltage across Z2 plus the base emitter voltageof Q3 establishes the on bias through resistors R2, and R4 for Q1. Thetemperature coefficients of Z2, Q1 and Q1 are known for given types andvoltage ratings of the devices and can be chosen to give a desiredcircuit temperature coefficient such as zero. D4, which is optional andmay be replaced by a short, is used to create a desired temperaturecoefficient of the firing point of the portion of the circuit includingQ1, Q2 and Q3. Because of the extreme temperature capability range ofthe combination of R2, R3, R4, R5, D4, Q1, Q2, Q3, and Z2 shown, thisunique circuit is very useful as a spark timing circuit for combustionengines. Another unique version of this invention is created byeliminating (shorting) Z2 and moving the upper R2 connection from thebase of Q3 to the cathode D1. This eliminates the voltage drop throughZ2 from point B and ground. References to ground in this application areintended to be only and aid in understanding this invention inreferences to the drawings shown, and could refer to any common point ofconnection of those components or common measurement point. It should berealized that one skilled in the state of the art might substitute othersemiconductor amplifying or switching devices for SCR1 in a particularapplication of the teaching of this invention and within the scope ofthis teaching, and that while the invention has been described in whatis presently considered to be a preferred embodiment, many modificationswill become apparent to those skilled in the art. It is intendedtherefore, by the appended claims to cover all such modifications as farwithin the true spirit and scope of the invention.

What is claimed is:
 1. A system for controlling the formation of a sparkin a combustion engine comprising:an alternator driven by said engineand having an alternating current output terminal; a semiconductorswitching device connected to said ignition control lead and having acontrol input terminal; a network having a network input terminal and anetwork output terminal; means connecting said network input terminal tosaid alternating current output terminal and said network outputterminal to said control input terminal so that said ignition system isdisabled above a selected engine speed; and a frequency sensitivecontrol network containing a frequency-to-current converter with meansto minimize the effect of changes in the output of said converter causedby changes of voltage of said alternating current output terminal. 2.The system of Claim 1 wherein said frequency sensitive control networkcomprises components requiring a source of direct current power, andmeans for obtaining direct current power by rectifying a portion of thevoltage applied to said control network input terminal.
 3. The system ofClaim 1 wherein said frequency sensitive control network has only threeterminals which comprise said control network input terminal, saidcontrol network output terminal, and a ground terminal.
 4. A frequencysensitive control network comprising:an input terminal for connection toa source of variable frequency alternating current; a filter capacitor;a first diode rectifying power from said input terminal to produce adirect current voltage of a first polarity across said filter capacitor;a second capacitor connected to be charged and discharged by apredetermined voltage difference during each cycle of said variablefrequency alternating current; a second diode connected from said secondcapacitor to ground and a third diode connected from said secondcapacitor to a summation point, said second and third diode polaritiessuch as to create a voltage on said summation point opposite to saidfirst polarity; and a path containing a resistor from said filtercapacitor to said summation point, said summation point being connectedto the input terminal of an amplifying diode having an input terminal,an output terminal and a common input/output terminal, said commoninput/output terminal being connected to ground and said output terminalimpedance to ground charging at a selected frequency of said alternatingcurrent.
 5. The network of Claim 4 wherein said amplifying device is ajunction field effect transistor.
 6. The network of Claim 4 wherein saidoutput terminal is connected to said filter capacitor through a secondresistor.
 7. The network of Claim 4 wherein said output terminalimpedance charge is used to remove the spark from a combustion engineabove said selected frequency.